If you enjoy outdoor winter sports, at some point you will be asking yourself, “When is it safe to go out on the ice?”

It’s not an easy question to answer, particularly this time of year. How quickly and how thickly a body of water freezes can depend on a variety of factors, including the depth and bottom topography of a waterway, weather cycles, currents, a water body’s size and the snow pack.

In order to understand how a lake freezes, take a look at how water freezes. As it cools, water contracts and gets denser. So one cup of water does not weigh the same at 80 degrees as it does at 40 degrees.

But where water reacts differently from most liquids is that starting at 39 degrees and cooler, it begins to expand and becomes less dense.

How does this affect your favorite lake or pond and when it freezes?

During the summer, you will find the colder, denser water near the bottom of a lake. This water, depending on the depth of the lake, can be in the low 40s. Warmer water is near the top, actually floating on top of the cooler water.

Many anglers have probably heard the term “turn over” in regard to a lake, usually in the sense that the lake needs to turn over before it freezes.

It means that as the water cools, it sinks because it is more dense, displacing the warmer water that floats towards the top, where it will then cool.

This process continues until the much of the lake is a consistent temperature.

Then as the water cools below 39 degrees, it begins to expand, and stays at the surface. As it further cools, molecules in the water start to slow down, and eventually they stop moving when the ice “catches” at 32 degrees, creating a solid.

That is why some of the bigger, deeper lakes, such as Sebago, take so long to freeze. At a length of 12 miles and a depth of over 300 feet, it takes quite a while for the entire lake to turn over and catch.

Once ice forms, it will continue to freeze if the temperature stays below 32 degrees.

Ice, and water for that matter, is a very poor insulator. That is why ice thickens as winter continues.

However, throw an insulating blanket of snow over the top of it, and it will slow down the freezing process. Several inches of snow will also create enough weight to partially submerge the ice, creating a slushy mess that can stop snowmobiles or ATVs in their tracks.

So when is the ice safe?

Ask different people and you will get different answers, even about the same lake. Take an ice chisel or auger, and you will see why.

At the season’s start, you will find that the ice in sheltered coves will be thicker. Out in deeper areas, the ice will be thinner. Near lake inlets, you will find the ice even thinner because of the current’s effects.

You can find ice that is 8 inches thick in one area and less than 3 inches just 10 feet away.

How thick does ice have to be in order to be safe?

There is no magic number, since ice quality can vary. Four inches of hard, newly frozen ice can support more weight than 12 inches of spring-thawed, honeycombed ice.

General guidelines for clear, newly formed ice are that 4 inches of ice is the minimum for activities such as ice fishing, skating or other activities on foot.

Wait to bring your ATV or snowmobile out on the ice until it is at least 5 inches thick, and if you are brave enough to bring your car or light truck out on the ice, look for 8 to 12 inches. Twelve to 15 inches should support a mid-sized truck.

So how can you tell if the ice is safe?

You can’t tell by just looking at it. You do have to drill or chop a hole to find out. And when measuring, don’t use that ruler that stretched your last trout to just a bit larger than your brother-in-law’s trout.

Be honest, and make sure that there is enough ice for you and your friends to enjoy a day out on the lake without worrying.

Mark Latti is a former public information officer for the Maine Department of Inland Fisheries and Wildlife and a registered Maine Guide. He can be reached at:

[email protected]